Sealless rotary blood pump

ABSTRACT

A rotary blood pump is provided which includes a pump housing and a rotor mounted for rotation with the housing. The rotor has an impeller. A rotor motor is provided including a plurality of permanent magnets carried by the impeller. A first motor stator is positioned on one side of the impeller and a second motor stator is positioned on an opposite side of the impeller. The motor stators each include a plurality of electrically conductive coils and pole pieces located within the housing. A plurality of wedge-shaped hydrodynamic thrust bearings are located outside of the axis of the rotor. During rotation of the impeller, the hydrodynamic bearings are separated from the housing by a fluid film and are not in direct mechanical contact with the housing.

[0001] This application is a continuation of application Ser. No.10/034,873, filed Dec. 26, 2001, to be issued as U.S. Pat. No.6,688,861, which is a continuation of application Ser. No. 09/689,251,filed Oct. 13, 2000, which is a continuation of application Ser. No.09/108,434, now U.S. Pat. No. 6,080,133, which is a division ofapplication Ser. No. 08/910,375, filed Aug. 13, 1997, now U.S. Pat. No.5,840,070, which is a continuation-in-part of application Ser. No.08/603,536, filed Feb. 20, 1996, now U.S. Pat. No. 5,695,471.

FIELD OF THE INVENTION

[0002] The invention relates generally to the field of blood pumps. Morespecifically, the invention pertains to continuous flow pumps of rotarydesign, suitable for permanent implantation in humans for use as chronicventricular assist devices.

BACKGROUND OF THE INVENTION

[0003] Thousands of heart patients who suffer from severe leftventricular heart failure could benefit from cardiac transplantation.However, owning to a shortage of donor hearts, most of these patientsface a foreshortened life span characterized by frequenthospitalizations, severe physical disability, and death from congestivefailure or cardiogenic shock. If a left ventricular assist device(“LVAD”) were available for chronic use, many of these patients could bereturned to prolonged and productive lives.

[0004] Prior art LVADs, now in clinical trials, provide a cyclic orpulsating delivery of blood, designed to emulate the natural pulsatileblood flow through the heart. This design approach has resulted in avariety of anatomic and engineering problems. Cyclic delivery systemstend to be physically large, making implantation difficult or impossiblefor some patients. Cyclic delivery systems tend to be physically large,making implantation difficult or impossible for some patients. Cyclicdelivery systems also employ artificial valves, having special material,longevity, and performance requirements. All of these characteristicsmake cyclic blood pumping device both complex and expensive.

[0005] It is apparent that if the requirement of pulsatile blood flow iseliminated, the LVAD could be much smaller, simpler, and less expensive.Rotary pumps, whether of centrifugal or axial flow design, providesubstantially continuous liquid flow, and potentially enjoy a number ofthe listed advantages over cyclic delivery systems. However, the priorart has not developed a durable rotary blood pump, owing to uniqueproblems with the rotary pump's driveshaft seal. In a blood environment,such driveshaft seals have a short life, and contribute to a prematurefailure of the pump. Prior art driveshaft seals may also causeembolisms, resulting in a stroke or even death for the patient.

[0006] Accordingly, it is an object of the present invention to providean improved rotary blood pump, by eliminating the necessity for adriveshaft seal;

[0007] It is a further object of the present invention to provide acompact, rotary blood pump using passive, magnetic radial bearings tomaintain an impeller and its support shaft for rotation about an axis;

[0008] It is yet a further object of the present invention to provide arotary blood pump having bi-stable operation, in which the impeller andthe support shaft shuttle as a unit, between two predetermined axialpositions;

[0009] It is another object of the present invention to provide bloodimmersed axial thrust bearings which are regularly washed by fresh bloodflow to prevent thrombosis from occurring;

[0010] It is yet another object of the present invention to provide aunique thick bladed pump impeller, which houses both motor magnets andradial bearing magnets, and includes narrow, deep, blood flow passages;

[0011] It is yet another object of the present invention to provide apump impeller which is effective pumping viscous liquids, such as blood,at low flow rates, and which minimizes hemolysis of the blood by usingonly a few pump impeller blades.

SUMMARY OF THE INVENTION

[0012] In accordance with illustrative embodiments of the presentinvention, a rotary blood pump includes a housing and a pump rotor. Acentrifugal pump impeller is attached to an impeller support shaft, orspindle, to form the pump rotor. The pump housing includes an elongatedinlet tube surrounding the shaft, and a scroll-shaped casing, or volute,with a discharge outlet, enclosing the impeller.

[0013] The shaft and the impeller are specially suspended within thehousing. Radial magnetic bearings of passive design, maintain thesupport shaft and the impeller about a rotational axis. The magneticbearing which levitates the shaft includes a plurality of permanent ringmagnets and pole pieces arranged along surrounding portions of the inlettube and a plurality of permanent disc magnets and pole pieces withinthe shaft itself. Radially adjacent pairs of these magnets are of likepolarity. One part of the magnetic bearing, which maintains the impellerabout a rotational axis, includes a plurality of permanent rod orarcuate magnets disposed in spaced, circular relation around bladesectors of the impeller; another part of the bearing includes a pair ofpermanent ring magnetos outside the casing, on either side of theimpeller. Adjacent portions of the rod and ring magnets are of oppositepolarity.

[0014] The shaft and impeller are axially restrained by a magnetic andhydrodynamic forces in combination with mechanical thrust bearings, ortouchdowns. The magnets of the magnetic bearing in the inlet tube andshaft may be arranged in slightly offset axial relation, to produce atranslational loading force, or bias, along the longitudinal axis of therotor. This bias substantially counteracts the axial force resultingfrom the hydraulic thrust of the rotating impeller. However, thehydraulic thrust will vary as a function of the cardiac cycle andadditional restraints are desirable to ensure that pump operation isstable and controlled. For this purpose, a pair of blood immersed thrustbearings is provided. These thrust bearings may be located at either endof the rotor, although other arrangements are feasible.

[0015] One thrust bearing is included at the upstream end of the supportshaft, and the other thrust bearing is located on the bottom, ordownstream side of the impeller. A spider within the inlet tube includesa touchdown, or thrust surface, against which the end of the shaftperiodically touches. Another touchdown is provided on an inner surfaceof the casing base, adjacent a downstream terminus of the impeller. Apredetermined amount of spacing is included between the two touchdowns,so as to allow the shaft/impeller assembly axially to shuttle back andforth, in response to the user's cardiac cycle. This shuttling motionwill produce a pumping action, frequently exchanging blood in thetouchdown area with fresh blood from the circulation. This pumpingaction minimizes the likelihood of blood thrombosis in the thrustregion, by maintaining the blood at an acceptable temperature and byshortening its residence time in the thrust bearing gap.

[0016] The impeller is of unique configuration and characteristics,owing to the special requirements of the present application. Contraryto conventional centrifugal pump design, the present invention usesrelatively few impeller blades, generally resembling pie-shaped sectors.Moreover, the blades are made quite thick in an axial direction, havingdeep and narrow, arcuate channels between adjacent blades for thepassage of blood through the impeller. The substantial height of theblades provides a relatively large blade working surface, ensuringefficient pump operation. These structural features decrease hemolysisof the blood, while containing useful efficiency in a pump using so fewimpeller blades.

[0017] Sealed, hollow chambers are provided within the thick impellerblades to reduce the density of the impeller. These chambers reducegravity induced loads on the thrust bearings, which in turn reduces thelikelihood of thrombosis of the blood used to lubricate the bearings.

[0018] The thick impeller blades are also used advantageously to housemagnets used in the pump drive system. Torque drive is imparted to theimpeller by magnetic interaction between arcuate, permanent magneticsegments imbedded within each impeller blade sector, and a circularelectromagnetic stator, affixed to the casing. Back-EMF sensing is usedto commutate the brushless motor stator, providing attractive andrepulsive forces upon the magnetic segments. A control unit and aportable power supply, worn on the user, power the pump drive system.The control unit allows the speed and drive cycle of the motor either tobe programmed or interactively determined by the user's physicalactivity or condition.

[0019] In certain embodiments of the invention, the motor includes aplurality of permanent magnets carried by the impeller and a motorstator including an electrically conductive coil located within thehousing. A ring of back iron is fixed to the casing to aid in completinga flux return path for the permanent magnets and to decrease the axialthrust which results from the attraction of the motor rotor magnetstoward the motor rotor stator. The impeller has a forward side facingthe inlet tube and a rear side downstream of the forward side. In oneembodiment, the conductive coil of the motor stator is located adjacentthe rear side of the impeller, and a stator back iron ring is locatedoutside of the conductive coil, within the housing and fixed to thehousing. In one embodiment, a second ring of back iron is located on theforward side of the impeller and outside of the casing but inside of thehousing, with the second ring of back iron being fixed to the casing. Inthat embodiment, a second motor stator having an electrically conductivecoil is located on the forward side of the impeller outside of thecasing but inside of the housing. In that embodiment, the second ring ofback iron is located forward of the second motor stator.

[0020] In certain embodiments, a plurality of hydrodynamic thrustbearings are located outside of the axis of rotation of the rotor. Thehydrodynamic bearings are wedge-shaped and, during rotation of the rotorand impeller, the hydrodynamic bearings are separated from the casing bya fluid film and are not in direct mechanical contact with the casing.

[0021] A more detailed explanation of the invention is provided in thefollowing description and claims, and is illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a left front perspective of the blood pump of thepresent invention;

[0023]FIG. 2 is a fragmentary, cross-sectional view of the pump of FIG.1, showing a plurality of ring magnets comprising part of the magneticbearing assembly;

[0024]FIG. 3 is a fragmentary, cross-sectional view of the pump of FIG.1, showing the shaft and an impeller;

[0025]FIG. 4 is a view as in FIG. 1, but with the shaft and impellershown removed from the housing;

[0026]FIG. 5 is a simplified, fragmentary, representation of a humanheart, showing the pump implanted within the left ventricle of theheart;

[0027]FIG. 6 is a transverse, cross-sectional view of the housing,impeller, and impeller chamber, taken along the line 6-6, shown in FIG.1;

[0028]FIG. 7 is a longitudinal, cross-sectional view of the pump, takenalong the line 7-7, shown in FIG. 1;

[0029]FIG. 8 is a longitudinal, cross-sectional view of a simplified,schematic representation of the pump, showing respective polarities ofthe magnets and the pole pieces of the passive radial magnetic bearings,and the elements of the pump motor, including rotor magnets and a motorstator;

[0030]FIG. 8a is a schematic view, similar to FIG. 8, but showinganother embodiment of the present invention;

[0031]FIG. 8b is a schematic view, similar to FIG. 8a, but showinganother embodiment of the present invention.

[0032]FIG. 9 is a longitudinal, cross-sectional view of an impellerconstructed in accordance with the principles of the present invention;

[0033]FIG. 10 is an end view thereof, taken from the right side of FIG.9;

[0034]FIG. 11 is a longitudinal, cross-sectional view of a simplified,schematic representation of another embodiment of the pump;

[0035]FIG. 11a is an enlarged view of the circled portion 11 a from FIG.11;

[0036]FIG. 12 is a cross-sectional end view of the FIG. 11 pump with theend of the housing and casing removed for clarity;

[0037]FIG. 13 is a perspective view, partially broken for clarity, ofthe blood pump of FIG. 11;

[0038]FIG. 13a is a perspective view of a portion of FIG. 13, showingthe slotted motor-stator;

[0039]FIG. 13b is a perspective view, similar to FIG. 13a but showing aslotless motor stator.

[0040]FIG. 14 is another perspective view, partially broken for clarity,of the blood pump of FIG. 11;

[0041]FIG. 15 is a longitudinal, cross-sectional view of anotherembodiment of the pump;

[0042]FIG. 15a is an enlarged view of the circled portion 15 a from FIG.15;

[0043]FIG. 16 is a cross-sectional end view of the FIG. 15 pump, withthe end of the housing and casing removed for clarity;

[0044]FIG. 17 is a longitudinal, cross-sectional view of anotherembodiment of a blood pump;

[0045]FIG. 17a is an enlarged view of the circled portion 17 a from FIG.17;

[0046]FIG. 18 is a cross-sectional end view of the FIG. 17 pump, withthe end of the housing and casing removed for clarity;

[0047]FIG. 19 is a longitudinal, cross-sectional view of anotherembodiment of the present invention;

[0048]FIG. 19a is an enlarged view of the circled portion 19 a from FIG.19; and

[0049]FIG. 20 is a cross-sectional end view of the FIG. 19 pump, withthe end of the housing and casing removed for clarity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0050] Turning now to FIGS. 1-8 of the drawings, a sealless rotary bloodpump 11 includes a housing 12, having an elongated inlet tube 13 and animpeller casing volute 14. A discharge tube 16 extends through thehousing to communicate with the interior periphery of casing 14. Tube 16has a tangential orientation with respect to a radius of the casing, foreffectively channeling the blood output from the pump.

[0051] A pump rotor 17 is located within housing 12, within casing 14,and includes an elongated, right-circular cylindrical support shaft orspindle 18, attached to a disc-shaped impeller 19. Rotor 17 is mountedfor rotation about a longitudinal axis which extends both through shaft18 and impeller 19. It should be noted that the preferred embodimentdisclosed herein includes an impeller and a casing of centrifugaldesign. However, many of the structural features and aspects ofoperation of the present invention may also be adapted advantageously torotary blood pumps of axial flow design.

[0052] The pump 11 of the present invention includes a forward magneticbearing 21 and a rearward magnetic bearing 22 to levitate rotor 17 andmaintain it in proper radial alignment with respect to its longitudinalaxis. A radial magnetic bearing construction is shown in U.S. Pat. No.4,072,370, issued to Wasson. The '370 patent is hereby expresslyincorporated by reference. The forward magnetic bearing 21 herein may beconstructed entirely in accordance with the teachings of the '370patent. However, several simplifications and improvements to theconstruction shown in the '370 patent are disclosed herein. For example,it has been determined that the radially polarized ring magnets(numerals 44 and 46) of the '370 device, are not necessary forsuccessful practice of the invention herein. In addition, as will beexplained below, the axially magnetized ring magnets (numeral 22) of the'370 device may advantageously be replaced with axially magnetized discmagnets for purposes of the present invention.

[0053] Accordingly, the forward magnetic bearing 21 includes a pluralityof rings, comprising ferromagnetic pole pieces 23 and axially polarizedpermanent magnets 24. As shown most clearly in FIGS. 7 and 8, polepieces 23 and magnets 24 are arranged in contingent, alternatingfashion, and are located between outer sidewall 26 and inner sidewall 27of inlet tube 13. The polarization of opposing magnets is the same,inducing an identical polarization into a respective pole piecetherebetween. A combination of high strength adhesive and surroundingtube sidewalls, maintains the arrangement of magnets and pole pieces incontingent relation, despite strong magnet forces attempting to urge therings apart.

[0054] Forward magnetic bearing 21 also includes a plurality of discs,comprising ferromagnetic pole pieces 28 and axially polarized permanentmagnets 29. Pole pieces 28 and magnets 29 are also arranged incontingent, alternating fashion, so as to form a magnetic structurewhich mirrors the polarity and axial position of respective pieces andmagnets of the surrounding rings. This magnetic structure is firstassembled and secured together using high strength adhesive, and is theninstalled within the hollow volume of shaft or spindle 17. The magneticpolarizations and repulsive forces produced by the magnets and the polepieces of forward magnetic bearing 21 are such that magnetic levitationof support shaft 18 results.

[0055] To provide additional radial restraint for rotor 17, rearwardmagnetic bearing 22 is also provided. Bearing 22 includes a first ringmagnet 31 mounted on an outer wall of casing 14, and a second ringmagnet 32 imbedded within a circular casing base 33. The bottom portionof casing 14 is attached and sealed to base 33, to form a fluidimpervious enclosure for impeller 19 (see FIG. 7). Both magnets 31 and32 are axially polarized, but each has a different polarization facingimpeller 19. Bearing 22 also includes a plurality of rod magnets 34,transversely extending from an upper face portion 36 to a lower faceportion 37 of impeller 19. Rod magnets 34 are arranged in spaced,circular fashion, adjacent an outer periphery 38 of impeller 19. Thepolarizations between the ends of magnets 34 and the adjacent surfacesof magnets 31 and 32 are respectively opposite, creating attractive, butequal and opposite magnetic forces acting on the impeller. It can beseen that radial movement of the impeller (deflection from the axis ofrotation) will result in a restoring force due to the attraction betweenthe magnets 34 towards magnets 31 and 32. The magnetic force in theaxial direction will largely be counterbalanced to the opposing magneticattraction of magnets 34 to magnet 31 and magnets 34 to magnet 32.However, the action of the magnetic force in the axial direction wouldnot be restoring.

[0056] It should also be noted that other configurations, locations,numbers, and polarization orientations may be used for the componentsforming rearward magnetic bearing 22. For example, magnets 34 may bearcuate segments, rather than rods. Also, the polarizations of themagnets 31, 32, and 34 may be arranged to effect respective repulsiveforces, rather than the attractive forces specifically disclosed herein.In this manner, referring to FIGS. 8a and 8 b, the south pole of magnets34 would be adjacent the south pole of magnet 31 and the north pole ofmagnets 34 would be adjacent tire north pole of magnet 32. For themagnets to be restoring in the radial direction, the magnets would haveto be offset. To this end, in the FIG. 8a embodiment magnets 34 would bemore outward radially than magnets 31 and 32. Alternatively, in the FIG.8b embodiment magnets 34 are radially inside the radial dimension ofmagnets 31 and 32. If a repulsive configuration is used, as illustratedin FIGS. 8a and 8 b, the action of the magnetic force would be restoringin both the radial and axial direction.

[0057] Although the drawings show magnets 32 and 34 as if portionsthereof are directly immersed in blood, in actual practice, athin-walled non-magnetic jacket or a plastic coating would be placedover these portions, to prevent contact between the magnets and theblood. Such contact, if it were allowed, would likely cause anundesirable chemical reaction, to the detriment of the blood. However,for clarity, the referenced jacket or coating, is not shown in thedrawings.

[0058] To provide mechanical limitations on axial, translationalexcursions of the rotor, a first thrust bearing 39 and a second thrustbearing 41 are provided. First thrust bearing 39 includes a threadedplug 42, installed within casing base 33. Plug 42 is screw adjustablealong the longitudinal axis of rotor 17, and includes a recessed bearingsurface 43. Surface 43 is contoured to accommodate a correspondingbearing tip 44, in the lower face portion of impeller 19. It should benoted that the particular configuration of bearing 39 is not critical,and planar bearing surfaces may alternatively be used in thisapplication.

[0059] Second thrust bearing 41 is secured within the blood entry end ofinlet tube 13, and includes a spider 46, adjustment knob 47, and ball48. Rotation of knob 47 will translate ball 48 along the longitudinalaxis of rotor 17.

[0060] Alternative locations and constructions for second thrust bearing41 are also contemplated. For example, an annular thrust bearing surfacecould be provided on the inner wall of casing 14, adjacent the upperface portion 36 of impeller 19. In this arrangement, portion 36 wouldslidably contact the annular thrust bearing surface. By eliminatingspider 46 and the associated components of the upstream thrust bearing,the possibility of blood deposits forming on these structures would beeliminated.

[0061] It will be appreciated that thrust bearings 39 and 41 areeffective not only to provide limit stops to axial movement of rotor 17,but also to adjust certain operational aspects of the pump. In thedrawings, the upstream end of support shaft 18 is shown in contact withball 48. However, this will not always be the case during the course ofoperating the pump. For example, it is desirable for the two thrustbearings to be adjusted so that the distance between them, is slightlygreater than the overall length of the rotor. This will allow the rotorto “shuttle”, back and forth between the axial constraints provided bythe thrust bearings with each cardiac cycle of the user. Each such cyclewill produce a pumping action, bringing fresh blood into the touchdown,or thrust bearing area.

[0062] The present invention does not use a journal bearing to restrainthe rotor. Of necessity, a journal bearing radially encases at least aportion of the rotor's support shaft or spindle. It is within this thin,annular volume between the shaft and the bearing surface, wherethrombosis can occur in prior art devices as a consequence of heat andexcessive residence time within the bearing. The bi-stable operation ofthe pump and rotor of the present invention, continuously flushes theblood around each thrust bearing, avoiding thrombosis effects of priorart journal bearings.

[0063] There is also an important physical relationship which existsbetween the rotor and the magnetic bearings of the device disclosedherein. This relationship is established and maintained by proper axialplacement of the adjustable thrust bearings. In operation of the pump,the pressure gradient produced by the rotating impeller imparts anupstream axial force on the rotor. This force needs to be substantiallycounterbalanced, to ensure that cardiac pulses will create sufficientpressure variances through the pump, to effect bi-stable operation. Byadjusting the axial relationship of the pole pieces 23 and the magnets24 with respect to the pole pieces 28 and magnets 29, a downstream axialforce will be produced. Since the forces within forward magnetic bearing21 are repulsive, the desired downstream loading or bias will beeffected when the magnets and pole pieces within the shaft aretranslated slightly downstream from the magnets and pole pieces in theinlet tube (See, FIGS. 7 and 8). Thus, second thrust bearing 41 iseffective to shift, or offset the rotor downstream a sufficient amountso the resultant, repulsive magnetic forces substantially counterbalancethe hydrodynamic axial force produced by the rotating pump impeller.

[0064] We can now turn to the special design considerations andoperational characteristics of impeller 19. As will be notedparticularly in FIG. 6, the impeller includes a plurality of large bladesectors 49. Owing to its relatively high viscosity and susceptibility todamage from heat and mechanical action, blood is a uniquely difficultliquid to pump.

[0065] It is generally preferable in a large centrifugal pump, to have asubstantial number of thin, sharp impeller blades with relatively largevoids or passages, between the blades, for the passage of low viscosityliquid. However, such a conventional design is not desirable, for asmall centrifugal pump which has to pump a viscous liquid, such asblood.

[0066] When blood flows axially into the leading edges of impellerblades it tends to be damaged by the mechanical action and turbulenceassociated with the impeller blades. Thus, one of the designconsiderations of the present invention is to reduce such hemolysis, byminimizing the number of impeller blades and leading edges.

[0067] To maintain efficiency in a small pump with so few blades, theeffective working area of the blades needs to be increased. This wasaccomplished in the present design by modifying the size andconfiguration of conventional blades in two significant aspects. First,blade sectors 49 are made relatively wide or expansive through arotational aspect (see FIG. 6). In other words, the outer periphery ofeach blade sector 49 assumes approximately 80 to 85 degrees of rotation.It should be noted that an alternative design contemplated hereinincludes only two blade sectors, each of which assumes approximately 175degrees of rotation. In either case, the width of the impeller bladesectors of the present invention differ significantly from known priorart blades.

[0068] The second modification pertains to the thickness or height ofthe blade sectors. As shown particularly in FIGS. 4 and 7, blade sectors49 are relatively thick in an axial direction. As a consequence of thesemodifications, a narrow and deep impeller blood flow path or passageway51 is defined between adjacent edges of blade sectors 49. By increasingthe thickness of the blade sectors and narrowing the blood passageway,the ratio between the area of working surface of the blades and thevolume of the passageway is increased. Also, the average distance of theliquid in the passageway from the working surface of the blades isdecreased. Both of these beneficial results provide a small pump forblood which has few blades for damaging blood, yet maintains acceptableefficiency.

[0069] The size and configuration of the impeller blades also allows thestructural integration of a number of features directly within theimpeller 19. For example, the previously discussed rearward magneticbearing 22 includes a plurality of rod magnets 34 of considerablelength. Owing to the thickness of the blade sectors, these magnets arereadily accommodated within the sectors. The sectors may also beprovided with respective hollow chambers 52, to reduce the mass of theimpeller and the gravity induced loads on the thrust bearings (see, FIG.6).

[0070] Lastly, a brushless rotor motor 53 include arcuate magneticsegments 54, imbedded within the upper face portion 36 of blade sectors49. As discussed above, the portions of segments 54 which wouldotherwise be in fluid communication with the pumped blood, are encasedin a jacket or a coating (not shown) to prevent any chemical reactionbetween the blood and the magnetic segments. Making reference to FIGS. 6and 8, segments 54 have alternating orientations in their polarities,and are directed toward an adjacent motor stator 56. Included withinstator 56 are windings 57 and a circular pole piece or back iron 58,mounted on the outer surface of impeller casing 14. Windings 57 areinterconnected by means of percutaneous wires to a controller 59 and apower supply 61, as shown in FIG. 5. Alternative to using wires,transcutaneous power transmission could be used. It is contemplated thatcontroller 59 and power supply 61 may be worn externally by the user, oralternatively, they may be completely implanted in the user.

[0071] Controller 59 may include circuitry as simple as a variablevoltage or current control, manually adjusted or programmed to determinethe running rate of pump. However, controller 59 may also haveinteractive and automatic capabilities. For example, controller 59 maybe interconnected to sensors on various organs of the user,automatically and instantaneously to tailor operation of the pump to theuser's physical activity and condition.

[0072] The windings 57 are energized by the electrical output ofcontroller 59 to produce an electromagnetic field. This field isconcentrated by pole piece 58, and is effective to drive magnets 54 andthe rotor 17, in rotary fashion. The back EMF resulting from the magnets54 passing by the windings is detected by the controller. The controlleruses this back EMF voltage to continue generation of the electromagneticfield in synchronism with further rotation of the rotor. Brushlessoperation of the motor 53 is effected, then, by electromagneticinteraction between the stator and magnets imbedded within the pump'simpeller blades.

[0073] Motor 53, with windings 57 and pole piece 58, together withmagnets 54, function not only to transmit torque but also provide arestoring radial magnetic force that acts as a radial bearing. Asillustrated in FIGS. 7 and 8, magnets 54 are carried by blade sectors 49and are positioned in radial alignment with pole piece 58. The magnets54 have attraction with the iron pole piece 58 of the stator. Anyattempt to deflect the impeller radially produces an increasingrestoring force between the pole piece 58 and the magnets 54 which wouldcause the impeller to return to a neutral position.

[0074] Rotation of the rotor 17, including shaft 18 and impeller 19,causes blood to flow through inlet tube 13 in the direction of arrows62. The blood continues its path from the upper edge of passage 51 tothe interior of casing 14. Discharge tube 16 allows the blood to beexpelled from the casing an into the user's cardiovascular system.

[0075] Anatomical placement of the pump 11 is shown in FIG. 5. Thesimplified representation of a human heart 63, includes a left ventricle64 and an aorta 67. The inlet tube 13 serves as the inflow cannula andis placed into the apex of the left ventricle 64. An arterial vasculargraft 66 is connected on one end to tube 13 and on the other end to theaorta 67 through an end to side anastomosis.

[0076] The centrifugal design of the pump allows a considerable amountof flexibility during implantation. Owing to the axial inflow and radialoutflow of the pump, a 90 degree redirection of the blood is effectedwithout the necessity of a flow-restrictive elbow fitting. Moreover, thepump can be rotated on its longitudinal axis to adjust the orientationof the discharge tube and minimize kinking and hydraulic losses in thevascular graft. Good anatomic compatibility is possible since the pumpcasing is compact and disc-shaped, fitting well between the apex of theheart and the adjacent diaphragm.

[0077] In a specific example although no limitation is intended,referring to FIG. 7, blood flow path 62 a is 0.06 inch to 0.1 inch inthickness. The fluid gap 70 comprising the clearance between theimpeller and the housing is 0.005 inch to 0.02 inch. The impellerdiameter is 1.0 inch to 1.5 inch. The rotor diameter is 0.025 inch to0.4 inch. The outside diameter of the flow annulus is 0.35 inch to 0.55inch. The outer diameter of the housing adjacent the forward end of thepump is 0.85 inch to 1.25 inch. The axial length of the entire pump is1.75 inch to 3.0 inch. The axial length of the rotor spindle is 1.0 inchto 1.5 inch and the axial length of the impeller is 0.2 inch to 0.5inch. By using a thick impeller (having a long axial length) the fluidgap 70 can be larger and still provide a highly efficient pumpingaction.

[0078] Enlarged views of an impeller used in the pump of the presentinvention are set forth in FIGS. 9 and 10. Referring to FIGS. 9 and 10,an impeller 74 is shown therein having a number of blade sectors 76, 78and 80. Blade sectors 76 and 78 are separated by slot 82; blade sectors78 and 80 are separated by slot 84; and blade sectors 80 and 76 areseparated by slot 86. By utilizing blade sectors 76, 78 and 80 that arerelatively thick in the axial direction, narrow and deep impeller bloodflow paths are formed by slots 82, 84 and 86 between the adjacent edgesof the blade sectors. By increasing the thickness of the blade sectorsand narrowing the blood passageway, the ratio between the area ofworking surface of the blades and the volume of the passageway isincreased. Also, the average distance of the liquid in the passagewayfrom the working surface of the blades is decreased. Both of thesebeneficial results allow a small pump for blood which has less bladesfor potentially damaging blood, yet the small pump maintains acceptableefficiency.

[0079] As a specific example although no limitation is intended, thediameter of the impeller is 1 inch to 1.5 inch, the blade depth bd (FIG.9) is 0.2 inch to 0.5 inch the magnet width mw (FIG. 9) is 0.15 inch to0.3 inch, the spindle diameter sd (FIG. 9) is 0.25 inch to 0.5 inch, andthe inner diameter id (FIG. 9) of the impeller inlet is 0.45 inch to 0.6inch. The width w of the slots (see FIG. 10) is approximately 0.075 inchand preferably ranges from 0.05 inch to 0.2 inch. The outlet angle a(FIG. 10) preferably ranges between 30° and 90°.

[0080] Another benefit of the thick impeller is the ability to utilizemagnetic pieces 88 that are inserted in a manner enabling the stators tobe on opposite sides of the impeller. Referring to FIGS. 11, 11a, 12, 13and 14, the blood pump 11′ shown therein is similar in many respects toblood pump illustrated in FIGS. 1-8, and includes housing 12 having anelongated inlet tube 13 and a scroll-shaped impeller casing or volute14. A discharge tube 16 extends through the housing to communicate withthe interior periphery of casing 14. Tube 16 has a tangentialorientation with respect to a radius of the casing, for effectivelychanneling the blood output from the pump.

[0081] Pump rotor 17 is located within housing 12, within casing 14, andincludes an elongated, right-circular cylindrical support shaft orspindle 18, attached to impeller 74. Rotor 17 is mounted for rotationabout an longitudinal axis which extends both through shaft 18 andimpeller 74.

[0082] The magnetic bearings for levitating rotor 17 and maintaining itin proper radial alignment with respect to its longitudinal axis are notspecifically shown but may be identical to those illustrated in the pumpembodiment of FIGS. 1-8 and described above.

[0083] In the FIGS. 11-14 embodiment, a first motor stator 90,comprising conductive coils or motor windings 91, is located at the rearof impeller 74. A ring of back iron 92 is located behind windings 91and, as illustrated in FIG. 1 first motor stator 90 and back iron 92 arefixed between housing 12 and casing 14.

[0084] A second motor stator 94, comprising windings 95, is positionedon the forward side of impeller 74. As illustrated in FIG. 11, windings95 are fixed to casing 14 and a ring of back iron 96 is positionedforward of windings 95. As illustrated in FIGS. 13, 13A and 14, backiron 92 and back iron 96 have teeth 98 which extend into the statorwindings to form the stator iron. Thus the windings 95 wrap around theteeth 98 in the intervening slots 99 (See FIG. 13a). In the FIG. 13bembodiment, a slotless motor stator is illustrated. In that embodiment,the windings 91 are fixed to the back iron 96 and there are no teethextending into the stator windings.

[0085] It can be seen that the motor stators 90 and 94 are placed onopposite sides of casing 14 such that each is adjacent to the pole facesof the motor rotor magnets 98. Back iron 92 and back iron 96 serve tocomplete a magnetic circuit. The windings 91 and 95 of the stators 90,94 can be in series or each stator 90, 94 can be commutated independentof the other. There are several advantages to this approach:

[0086] First, as long as the pole faces of the motor rotor magnets arecentered between the faces of the motor stators, the net axial forcewill be relatively low.

[0087] Second, the radial restoring force which results from theattractive force of the motor rotor magnets to the motor stators will benearly twice as large as the restoring force with only one stator. Thetotal volume and weight of the motor will be smaller than a singlestator design.

[0088] Third, the dual stator design is adapted to provide systemredundancy for a fail safe mode, since each stator can be made tooperate independently of the other in the case of a system failure.

[0089] Fourth, hydrodynamic bearings can be located on the surface ofthe impeller to constrain axial motion and to provide radial support inthe case of eccentric motion or shock on the device. Referring to FIGS.11 and 11a in particular, hydrodynamic bearings in the form of raisedpads 100, 101 and contact surfaces 102 and 103 are illustrated. Suchhydrodynamic bearings are symmetrically located about the impeller asillustrated in FIG. 13, in which raised pads 100 are shown.

[0090] The raised pads could be rectangularly-shaped or wedge-shaped andare preferably formed of hardened or wear resistant materials such asceramics, diamond coating or titanium nitride. Alternatively, the raisedpads may be formed of a different material having an alumina or otherceramic coating or insert.

[0091] The raised pads are carried by either the impeller or the casing,or an attachment to the casing. In the FIGS. 11 and 11a embodiment, theraised pads 100 are carried by the impeller and the raised pads 101 arecarried by a cup-shaped member 104 that is fastened to the casing.Cup-shaped member 104 is utilized as a reinforcement for the casingwhich would not be structurally stable enough to carry the raised padsitself.

[0092] The hydrodynamic bearings are formed by a raised pad spaced froma contact surface by the blood gap. Although at rest there may becontact between the impeller and the casing, once rotation begins eachhydrodynamic bearing is structured so that during relative movementbetween the raised pad and the contact surface the hydrodynamic actionof the fluid film produces increased pressure within the bearing gapwhich forces the raised pad and the contact surface apart.

[0093] Depending upon the location of the hydrodynamic bearings, theycan aid in axial support, radial support or both axial and radialsupport. For example, if the bearings are perpendicular to therotational axis, they aid primarily in axial support but if they are atan angle with respect to the rotational axis, they aid in both radialand axial support. In the embodiment of FIGS. 11-14, the hydrodynamicbearings are positioned outside the axis of rotation, as illustrated.

[0094] In the FIGS. 15-16 embodiment, there is a single axial motor andthe stator 90 is located at the rear end of impeller 74. Stator 90comprises windings 91, and a ring of back iron 92 is located downstreamof windings 91. The motor stator 90 and back iron are fixed betweencasing 14 and housing 12.

[0095] In the FIGS. 15-16 embodiment, a ring of back iron 106 is placedin the impeller, in axial alignment with the magnets, such that itcompletes the flux return path for the motor rotor magnets in theimpeller. Thus while motor stator 90 and back iron 92 are locateddownstream of the impeller and outside of casing 12, back iron 106 islocated within the impeller and within the casing 12. Using back iron tocomplete the magnetic circuit in this manner increases the overallefficiency of the motor.

[0096] Referring to the embodiment of FIGS. 17-18, a motor stator 90 andback iron 92 are provided at the rear end of impeller 74 as with theFIGS. 9-14 embodiments, but another ring of back iron 108 is placedoutside pump casing 12 on the front side of the impeller and is fixed tothe casing. Back iron ring 108 serves two purposes. First, it serves tohelp complete the flux return path for the motor rotor magnets. Second,the attractive force between the motor rotor magnets and the ring ofback iron 108 substantially reduces the net axial force produced by theattraction of the motor rotor magnets for the stator iron. Third, thering of back iron significantly increases the radial restoring forcecompared to just the interaction between the motor rotor magnets and thestator iron.

[0097] Although the FIGS. 1-18 embodiments utilize an axial flux gapmotor, in the FIGS. 19-20 embodiment a radial flux gap motor isutilized. To this end, a ring-shaped structure is placed on either sideof the impeller to house a series of motor rotor magnets (an evennumber) oriented such that the magnetic poles of the motor rotor magnetsare radially, and alternately, aligned. The inner diameter of themagnets is located on the surface of a ring of back iron to provide aflux return path. On the opposite end of the impeller, passive radialmagnetic bearings are used.

[0098] It can be seen that in the FIG. 19-20 embodiment the motor rotormagnets 110 are radially aligned. Radially within the motor rotormagnets 110 is a ring of back iron 112. The inner diameter of magnets110 are located on the surface of back iron ring 112 (see FIG. 20) toprovide a flux return path. The motor rotor magnets 110 and ring of backiron 112 are carried by the impeller within the casing 14. Outside ofthe casing 14 there is radially positioned a ring-shaped stator 114 withmotor windings 116.

[0099] A number of axial permanent magnets 120 are carried by theimpeller, at its rear end. A number of axial permanent magnets 122 arefixed to the casing 14 and housing 12, downstream of and partiallyoffset from, magnets 120. Magnets 120 and 122 serve as passive magneticbearings for the impeller.

[0100] There are two significant differences from axial flux gap motorsby using the radial flux gap motor. First, there is very little axialforce produced by the interaction between the motor rotor magnets andthe stator. Second, there is no restoring force with the radial flux gapmotor. Radial support is provided by mechanical bearings or dedicatedradial magnet bearings.

[0101] It will be appreciated, then, that I have provided an improvedsealless blood pump including magnetic bearings and thrust bearingsuspension to minimize thrombosis, and an impeller having a blood flowpath therethrough which is calculated to minimize hemolysis.

[0102] Various elements from the FIGS. 1-8 embodiment can be used in theFIGS. 11-20 embodiments. For example, magnets 34 illustrated in FIGS. 3and 4 could be used in impeller 74 of the FIGS. 11-20 embodiments. Also,rotor 18 of the FIGS. 11-20 embodiments could be supported using frontthrust bearings such as thrust bearing 41 of the FIGS. 1-8 embodiment.Various other elements may be employed in the FIGS. 11-20 embodimentsfrom the FIGS. 1-8 embodiment.

[0103] Although illustrative embodiments of the invention have beenshown and described, it is to be understood that various modificationsand substitutions may be made by those skilled in the art withoutdeparting from the novel spirit and scope of the present invention.

What is claimed is:
 1. A rotary blood pump, comprising: a pump housing;a rotor mounted for rotation within said housing, said rotor having animpeller; a rotor motor, said motor including a plurality of permanentmagnets carried by said impeller; a first motor stator positioned on oneside of said impeller and a second motor stator positioned on anopposite side of said impeller; said motor stators each including aplurality of electrically conductive coils and pole pieces locatedwithin said housing; a plurality of wedge-shaped hydrodynamic thrustbearings located outside of the axis of rotation of said rotor; andduring rotation of the impeller the hydrodynamic bearings are separatedfrom the housing by a fluid film and are not in direct mechanicalcontact with the housing.
 2. A rotary blood pump as defined in claim 1,in which said hydrodynamic bearings are arcuate and are located on theforward side of said impeller.
 3. A rotary blood pump as defined inclaim 1, in which at least some of said hydrodynamic thrust bearings arecarried by said impeller.
 4. A rotary blood pump, comprising: a pumphousing; a rotor mounted for rotation within said housing, said rotorhaving an impeller; said impeller having large axially thick bladesectors; a rotor motor, said motor including a plurality of permanentmagnets carried by said impeller; a first motor stator positioned on oneside of said impeller and a second motor stator positioned on anopposite of said impeller; said motor stators each including a pluralityof electrically conductive coils and pole pieces located within saidhousing; a plurality of wedge-shaped hydrodynamic thrust bearingscarried by said impeller and located outside of the axis of rotation ofsaid rotor; said hydrodynamic bearings being arcuate and being locatedon the forward side of said impeller; and during rotation of saidimpeller, the hydrodynamic bearings are separated from the housing by afluid film and are not in direct mechanical contact with the housing. 5.A rotary blood pump as defined in claim 4, in which said hydrodynamicbearings are arcuate and are located on the forward side of saidimpeller.